1. Field of the Invention
The present invention relates to a photomask having a transcribing pattern, and more particularly, to a photomask having a transcribing pattern for obtaining a fine photoresist pattern surpassing a resolution limit of an exposure apparatus and a method of forming a photoresist pattern using the photomask.
2. Discussion of the Related Art
In general, a semiconductor device or a display device is fabricated by repeatedly performing a step of forming a thin film on a substrate through deposition, a step of forming a photoresist pattern on the thin film through coating and patterning a photoresist material and a step of forming a thin film pattern through etching the thin film.
The step of forming the photoresist pattern includes a step of coating the photoresist material on the thin film and a step of irradiating a light onto the photoresist material using a photomask having a transcribing pattern. The irradiation onto the photoresist material is performed by an exposure apparatus. The exposure apparatus may be classified into a proximate type and a projection type according to a distance between the photomask and the substrate. In the proximate type exposure apparatus, since the photomask and the substrate are disposed adjacent to each other, a resolution for the photoresist pattern is relatively low. In the projection type exposure apparatus, since an optic system including a plurality of lenses is disposed between the photomask and the substrate, a resolution for the photoresist pattern is improved.
Accordingly, it is preferable to use the projection type exposure apparatus for forming the photoresist pattern. However, since the projection type exposure apparatus has a high price and a low exposure speed as compared with the proximate type exposure apparatus, the proximate type exposure apparatus may be used based on the production cost.
A method of forming a photoresist pattern using a proximate type exposure apparatus will be illustrated referring to drawings hereinafter.
FIGS. 1A and 1B are cross-sectional views showing a method of forming a photoresist pattern according to the related art, and FIG. 2 is a plan view showing a photomask according to the related art.
In general, a transcribing pattern on a photomask has various shapes according to a type of a photoresist material. For example, since an exposed portion of a negative type photoresist material remains to become a photoresist pattern, a transcribing pattern of a photomask for the negative type photoresist material may be formed as a transmissive pattern that a light penetrates. Further, since a non-exposed portion of a positive type photoresist material remains to become a photoresist pattern, a transcribing pattern of a photomask for the positive type photoresist material may be formed as a shielding pattern that blocks a light.
In FIG. 1A, a photoresist (PR) film 14 is formed on a substrate 12 by coating a negative type photoresist material. The substrate 12 having the photoresist film 14 is transferred to a proximate type exposure apparatus (not shown) and a photomask 16 having a transcribing pattern 18 is disposed over the substrate 12. In the proximate type exposure apparatus, a distance between the photomask 16 and the substrate 12 may be kept to be several micrometers.
In FIG. 2, the transcribing pattern 18 having a stripe shape of a plurality of bars is formed on the photomask 16. Since the photomask 16 is used for a negative type photoresist material, a portion of the photomask 16 corresponding to the transcribing pattern 18 functions as a transmissive area where a light passes and the other portion of the photomask 16 except the transcribing pattern 18 functions as a blocking area which blocks a light. Each bar of the transcribing pattern 18 has a continuous region without discontinuity.
In FIG. 1B, a light is irradiated onto the photoresist film 14 (of FIG. 1A) on the substrate 12 to form a photoresist pattern 20. The photoresist pattern 20 on the substrate 12 has a similar shape to the transcribing pattern 18 of the photomask 16. In addition, a first width w1 of the transcribing pattern 18 is smaller than a second width w2 of the photoresist pattern 20. The difference between the first and second widths w1 and w2 may be defined as a critical dimension bias.
For example, when the photomask 16 that has the transcribing pattern 18 having the first width w1 of about 10 μm is used for the proximate type exposure apparatus, the photoresist pattern 20 may have the second width w2 of about 17 μm to about 20 μm. Accordingly, the proximate type exposure apparatus may have a critical dimension bias of about 7 μm to about 10 μm. The width of the photoresist pattern 18 may be influenced by an amount of exposure and a gap between the photomask 16 and the substrate 12.
When the proximate exposure apparatus is used, the second first width w2 of the photoresist pattern 20 on the substrate 12 may be adjusted by controlling the first width w1 of the transcribing pattern 18 of the photomask 16 or by controlling the amount of exposure and the gap. However, when the photoresist pattern 20 is designed to have the second width w2 smaller than about 7 μm, the transcribing pattern 18 may not be formed on the photomask 16 due to the critical dimension bias. Since the photoresist pattern 20 having the second width w2 smaller than about 7 μm is not obtained from the photoresist film 14 by using the proximate type exposure apparatus, the projection type exposure apparatus of a relatively higher price and a relatively longer exposure time is required for the photoresist pattern 20 having the second width w2 smaller than about 7 μm.